1. Field of the Invention
The present invention generally relates to fiber reinforced composites and methods for their manufacture and, in particular, to fiber reinforced composites which incorporate recycled thermoplastic.
2. Description of the Related Art
Thermoplastic reinforced with random glass mat (also referred to as glass mat thermoplastic or G MT is sold commercially in significant quantities (more than 200 million pounds per year). GMT is usually supplied as semi-finished sheets which are heated and compression molded to desired conformations. GMT is a very tough product with moderate stiffness that is used extensively by the automotive and construction industries. Typical automotive applications include battery trays, seats, station wagon loading doors, bumper beams, and sound shields.
GMT sheets are often commercially manufactured by a melt impregnation process. The glass fiber is typically either a swirled mat of continuous fiber or chopped fibers held together in a mat by a binder. GMT typically contains 20-50% by weight glass, more commonly about 30-40%. The matrix thermoplastic is commonly polypropylene (PP) although other thermoplastics are also used, such as polyamide-6,6 (nylon 66) and polyamide-6 (nylon 6) and polyethylene terephthalate (PET). Products are formed from GMT sheets by compression molding a process wherein sheets of GMT are layered to a desired thickness, heated and placed in or on a mold, and pressure is applied to shape the sheets into the shape of the mold.
Recycled thermoplastic can be derived from many sources. One of the more plentiful and less expensive sources is carpet, such as from manufacturing waste or pre or post consumer waste. Whole carpet waste is produced during manufacture from unsold merchandise, and from post consumer disposal. Typically, whole carpet comprises nylon, polypropylene or PET pile or tufts, at least one backing formed from one or more polyolefins, such as polypropylene, and an adhesive material of styrene-butadiene rubber (SBR) applied as a latex and filled with an inorganic filler such as calcium carbonate. If the carpet is obtained post use, it may also contain some amount of dirt. A typical carpet sample has a pile weight of about 40 oz. per square yard, a backing weight of about 8 oz. per square yard and an adhesive weight (SBR latex and filler) of 24 oz. per square yard. In other words, a nylon (or PET) carpet sample may comprise about 56% nylon (or PET), about 11% polypropylene, and about 33% SBR plus filler.
Single component carpet waste results during manufacture when the upper section of the carpet tufts are trimmed off, producing a waste material referred to as carpet lint or shear lint. Nearly pure single component waste can also be produced from separation processes, such as a separation process employed to recapture nylon. In such a process large amounts of polypropylene or other backing material may be recovered and there exists a need to find a suitable use for this material. Also, fiber waste is generated from the residual material left on tufting machines, from fiber spinning and from yarn preparation. It has become apparent in recent years that there is a need for finding uses for this, otherwise, discarded material.
Carpet recycling to form a thermoplastic composition is taught by David et al. in U.S. Pat. Nos. 5,294,384 and 5,591,802. The composition taught by David et al. is prepared by melt blending the carpet sample in an extruder which intensively mixes the components through high shearing stresses. The melt blend can then be cut into pellets, for example, or another useful and commercially acceptable form. It is taught that the melt blend can be used in applications requiring virgin thermoplastic material.
An article by Hugh C. Gardner of Amoco Fabrics & Fibers Company published in IFJ (August 1995), page 36, entitled "Carpet Recycling Technology," discusses compression molding two pieces of carpet with a glass mat to obtain a laminate structure. Gardner teaches the use of whole pieces of carpet which is impracticable because it requires discrete placement of the carpet and glass mat. Furthermore, Gardner's laminated structure would not lend itself to the normal mode of processing GMT, which is flow molding under compression, because the resin in the core would squirt out to fill the mold and uniform spreading of the glass fibers would not be achieved.
GE Plastics in Pittsfield, Mass. sells a continuous strand glass fiber reinforced polypropylene sheet under the trademarks AZDEL.RTM. SM10400 and AZDEL.RTM. PM10400. The sheet has a glass fiber content of about 40% by weight with the remainder being polypropylene resin. Other grades of AZDEL.RTM. are sold with different glass contents. However, product literature on AZDEL.RTM. does not teach or suggest the use of recycled thermoplastic or the use of nylon as the thermoplastic.
Therefore, there is a need to address these and other shortcomings of the prior art.